We have investigated magnetic field assisted implantations of 200 keV Xe-ions in 30-90 nm thick Fe 5 0 Co 5 0 alloy films on Si substrates at ion fluences of up to 1.3x10 1 6 cm - 2 . Longitudinal magneto-optic kerr effect measurements at room temperature suggest that the coercivity of the films first decreases for increasing ion fluence, while the magnetic remanence develops as a superposition of fourfold and twofold uniaxial anisotropies. Higher Xe-ion fluences increase the density of pinning centers therefore causing slight increases of the coercivity and of the magnetostrictive anisotropy. Lattice expansion and ion-induced grain growth were measured parallel to MOKE by X-ray diffraction.